Modern commercial, military, and civil space missions often utilize electric propulsion systems to benefit from the advantages offered by this mode of propulsion. Unlike chemical propulsion systems, which provide very high thrust levels over short durations of time, electric propulsion systems provide capabilities for prolonged low levels of continuous or pulsed thrust. Over time, the prolonged low thrust levels can offer more efficient operation than can chemical propulsion systems, particularly once a mission has entered the low-gravity environment of space. In many instances, the fuel requirements for electric propulsion systems are considerably lower than that of chemical propulsion systems, which can be highly desirable for increasing payload-carrying capabilities of a mission. Alternately, electric propulsion systems can offer considerably longer-term operation than can chemical propulsion systems utilizing similar quantities of fuel.
A number of design variations are available for electric propulsion systems. Regardless of their particular design, electric propulsion systems provide an outflow of high-energy ions or other energetic particles to affect a change in velocity of a spacecraft through conservation of momentum.
The energetic outflow of electric propulsion systems is also one of the primary challenges associated with their use. During operation of electric propulsion systems, the energetic outflow can impinge upon sensitive surfaces (e.g., solar panels or arrays, optical reflectors, sensors, antennas, and the like) of a spacecraft structure. Over time, repeated impacts of energetic particles upon such surfaces can sputter away protective thin-film coatings intended to dissipate charge from the environment, thereby leaving sensitive components susceptible to damage from electrostatic discharge (ESD). Other functional coatings can be similarly affected by repeated impacts of energetic particles. Loss of protective coatings or other similar coatings in this manner can compromise the operability of a spacecraft and ultimately lead to failure of a mission.
To address the foregoing issue, many current spacecraft designs mount the thrusters of an electric propulsion system at locations where their outflow is directed well away from sensitive surfaces. This can be sub-optimal from standpoints of both fuel efficiency and propulsion efficiency. For example, inefficient direction of the thrusters of an electric propulsion system can lead to a significant propellant penalty, ultimately leading to higher mission costs. Alternately, expensive transient protection units (TPUs) can be used to protect sensitive spacecraft components from electrostatic discharge. In fact, when sputtering-induced loss of a protective coating is expected to be unavoidable due to a particular thruster configuration being present, protective coatings are often not utilized at all in favor of TPUs. In either case, the amount of payload that can be transported by the spacecraft is decreased, since extra fuel needs to be carried to account for propulsion inefficiency or to accommodate the added weight of TPUs. Both of these factors can impact the economic viability of a mission. Further, TPUs are by themselves an expensive spacecraft component, and their use can add significantly to mission costs.
In view of the foregoing, the ability to utilize a broader range of thruster configurations in spacecraft incorporating an electric propulsion system would represent a substantial advance in the art. The present disclosure satisfies the foregoing need and provides related advantages as well.